import java.util.*;
/*
 * @lc app=leetcode.cn id=341 lang=java
 *
 * [341] 扁平化嵌套列表迭代器
 */

// @lc code=start
/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
interface NestedInteger {
    
    // @return true if this NestedInteger holds a single integer, rather than a nested list.
    public boolean isInteger();

    // @return the single integer that this NestedInteger holds, if it holds a single integer
    // Return null if this NestedInteger holds a nested list
    public Integer getInteger();

    // @return the nested list that this NestedInteger holds, if it holds a nested list
    // Return null if this NestedInteger holds a single integer
    public List<NestedInteger> getList();
}

public class NestedIterator implements Iterator<Integer> {
    private final Iterator<Integer> it;
    private List<Integer> ans;

    //NestedInteger相关的定义上面有了，我之前没咋细看
    public NestedIterator(List<NestedInteger> nestedList) {
        ans = new ArrayList<>();
        dfs(nestedList);
        it = ans.iterator();
    }

    public void dfs(List<NestedInteger> nestedList){
        for(NestedInteger ni : nestedList){
            if(ni.isInteger()){
                ans.add(ni.getInteger());
            }else{
                dfs(ni.getList());
            }
        }
    }

    @Override
    public Integer next() {
        return it.next();
    }

    @Override
    public boolean hasNext() {
        return it.hasNext();
    }
}

/**
 * Your NestedIterator object will be instantiated and called as such:
 * NestedIterator i = new NestedIterator(nestedList);
 * while (i.hasNext()) v[f()] = i.next();
 */
// @lc code=end

